Week 3: Electrical Theory; History of Recording
Electricity * High Voltage - Power (plugging into the wall for actual power) * Low Voltage - Connections between components Circuit A prescribed pathway for electrons to flow There are three states for a circuit to be in... # Closed - Circuit is on # Open - Circuit is off # Short - When there is something other than the prescribed pathway interrupting the flow Voltage Potential energy, energy at rest it is measured in “Volts”, this is the force that moves or pushes the electrons through the circuit. Resistance Something that causes work to be done by a circuit, resistance is measured in "ohms" (Ω) Current The amount of electrical energy that can safely move through a circuit, this is measured in amps. Wattage A measurement of how much work can be performed by a electrical circuit * W = V x A (watts equals volts times amps) * W = 120 x 20 (2400 watts can safely pass through) Ohms Law Often V = I (current) x R (resistance) = LOW VOLTAGE This does not require a license Impedance Measured by ohms, the letter "z" is often used to differentiate impedance from resistance. Impedance is frequency dependent resistance All gear has a impedance ratings. Low-impedance microphones are professional grade. They tend to use a standard XLR. Don't run a high-impedance microphone long distances. A trick to remembering impedance situations is this: * "Low into high won't fly." * "High into low won't go." Generally speaking, you want to go from your lowest impedance and scale up. Resistance - Measured by ohms Balanced Vs. Unbalanced You always need to know if you've got balanced or unbalanced cables, inputs, and outputs. If I have at minimum I'll have two wires, the hot and the ground. For example the Quarter-inch TS cable has the hot wire through the tip, and the ground attached to the sleeve. This is an unbalanced cable, and subject to RFI (Radio Frequency Interference) Balanced - Will have three wires, the hot wire, the cold cable, and ground. For example the quarter-inch TRS has the hot wire through the tip, the cold wire through the ring, and the ground through the sleeve. Using a balanced signal will boost your signal by about 3 dB, this is accomplished by sending your signal through the hot cable, and sending your signal inverted through the cold cable. Once it gets to the balancing amplifier the signal is switched back around to achieve the boost. An additional effect of this is that RFI picked up along the cable is flipped out of phase and is cancelled out. Direct boxes (DI) Can take high-impedance signal and turn it into low-impudence signal Can take a instrument level box into a mic level output. (+10dBv to -4dBm) Can take it unbalanced to balanced. A passive DI conditions the signal through a transformer. An active DI requires external power,either from a battery or phantom power (48v). Amplify - Increase the signal Attenuate - Decreases the signal.